This invention relates to supplying a mixture of augmenting compressed air and steam to a combustion turbine for power augmentation.
The output or capacity of a combustion turbine usually falls off with increasing temperature at the inlet to the compressor component. Specifically, the capacity of the compressor component to supply air to the combustion process and subsequent expansion through the turbine is reduced as the compressor inlet temperature is increased (usually due to increased ambient temperature). Thus, the turbine component and combustion component of the combustion turbine usually have the capability to accept more compressed fluid than the compressor component can supply when operating above a certain inlet temperature.
The present invention provides a design method for simple and combined cycle gas turbine power plants, to improve the output power during high ambient temperature operation. In particular, the invention concerns a method for increasing the mass flow through the turbine component or section by injection of a mixture of compressed air and steam at the gas turbine compressor discharge and/or in the combustion system, thereby improving the power output of the gas turbine power plant. In addition to power output, the thermodynamic efficiency is also improved in simple cycle gas turbine power plants.
Power augmentation of gas turbine cycles with steam injection has been done previously. However, the maximum amount of steam injection may be limited to a certain percentage of the air flow through the gas turbine compressor. The gas turbine compressor air flow naturally reduces as ambient temperature increases, and, hence, the potential amount of steam injection is limited.
The invention described herein, proposes to use an external motor driven compressor and steam generated using the energy of the turbine exhaust gases to inject a steam-air mixture at the gas turbine compressor discharge or in the combustion system to increase the mass flow through the gas turbine, and thereby increase the power output of the power cycle.
The purpose of the Steam Air Injection Cycle in accordance with this invention is for gas turbine power augmentation at high ambient temperature conditions. In addition to power augmentation, the heat rate is also reduced due to the use of gas turbine exhaust heat for steam generation. Power augmentation with steam injection may be limited by the maximum steam injection limits of the dry low NOx combustion system. The injection of air with the off-base compressor, however, provides additional power augmentation capability for the gas turbine.
The compressor may include a closed loop intercooling system, where the heat absorbed by the cooling water in the intercooler is rejected to the ambient via a cooling tower in the closed loop cooling water system. The compressor may also include inlet guide vanes for air flow control, a modulating blow-off valve to protect from surging during periods of low process demand, and protection for overload conditions by limiting the maximum air flow.
In one exemplary embodiment, the steam and air mixture is supplied directly to the inlet of the combustor. In this embodiment, the steam is generated in a waste heat boiler where the feed water entering the boiler is superheated to a temperature of xcx9c700xc2x0 F. The feed water flow control valve is modulated to control feed water flow to be equal to the gas turbine flow demand, up to the maximum steam injection limit for the given operating condition.
The superheated steam and the injection air is mixed in a mixing Tee prior to injection to the gas turbine combustor through the steam injection ports.
In a second embodiment, the mixture of steam and air is reheated in an upstream section of the heat recovery boiler before it is supplied to the combustor inlet.
In a third embodiment, the compressed discharge air from the external compressor is heated to xcx9c700xc2x0 F. in a downstream section of the heat recovery boiler before it is mixed with the superheated steam.
Before the steam-air mixture is actually admitted to the on-base manifold, all upstream piping must complete a preheat sequence. An improperly preheated steam-air mixture injection system can potentially deliver condensate to the combustors, which could extinguish the flame or damage hardware. To ensure adequate preheating of the steam-air mixture injection system, hot air from the off-base compressor may be used to preheat the system. The steam-air mixture will not be admitted to the machine until the preheat conditions are satisfied.
Accordingly, in its broader aspects, the invention relates to a land based gas turbine plant comprising a turbine compressor, a turbine section, and a combustor between the compressor and the turbine section; a heat recovery boiler incorporating at least one heat exchange section arranged to receive exhaust gas from the turbine section, the heat recovery boiler receiving water passed in heat exchange relationship with the exhaust gas to produce steam; and an external compressor for supplying augmenting combustion air, wherein the steam produced in the heat recovery boiler is mixed with the augmenting combustion air to produce a mixture of steam and air that is injected into the combustor.
In another aspect, the invention relates to a land based gas turbine plant comprising a turbine compressor, a turbine section, and a combustor between the compressor and the turbine section; a heat recovery boiler incorporating at least one heat exchange section arranged to receive exhaust gas from the turbine section; and means for increasing mass flow through the turbine section to thereby improve power output of the gas turbine plant.
In still another aspect, the invention relates to a method of increasing mass flow through a turbine section of a land based gas turbine plant that includes a turbine compressor, the turbine section and a combustor, the method comprising: a) supplying compressed air from an external compressor; b) supplying steam generated by water passing in heat exchange relationship with exhaust gases from the turbine section; c) mixing the compressed air from the external compressor with the steam; and d) supplying a mixture of the compressed air and the steam to the combustor.